HPCA Practice talk

RISC vs. CISC wars raged in the 1980s when chip area and
processor design complexity were the primary constraints and
desktops and servers exclusively dominated the computing land-
scape. Today, energy and power are the primary design con-
straints and the computing landscape is significantly different:
growth in tablets and smartphones running ARM (a RISC ISA)
is surpassing that of desktops and laptops running x86 (a CISC
ISA). Further, the traditionally low-power ARM ISA is enter-
ing the high-performance server market, while the traditionally
high-performance x86 ISA is entering the mobile low-power de-
vice market. Thus, the question of whether ISA plays an intrinsic
role in performance or energy efficiency is becoming important,
and we seek to answer this question through a detailed mea-
surement based study on real hardware running real applica-
tions. We analyze measurements on the ARM Cortex-A8 and
Cortex-A9 and Intel Atom and Sandybridge i7 microprocessors
over workloads spanning mobile, desktop, and server comput-
ing. Our methodical investigation demonstrates the role of ISA
in modern microprocessors’ performance and energy efficiency.
We find that ARM and x86 processors are simply engineering
design points optimized for different levels of performance, and
there is nothing fundamentally more energy efficient in one ISA
class or the other. The ISA being RISC or CISC seems irrelevant